There are many soft-tissue to bone repair procedures, such as rotator cuff, SLAP and Bankart lesion repairs, or reconstruction of labral tissue to the glenoid rim, in which a surgeon needs to secure tissue in close contact with bone by implanting an anchor, pre-loaded with suture, into a hole drilled in the bone at the desired anchor location. Commonly, the anchor which the sutures are attached to is made of either plastic such as PEEK or metal such as Titanium or Stainless Steel. Such anchors function like a nail or screw to secure them into the bone. Floating sutures, loaded into the rigid anchor body, are then passed through soft tissue near the anchor and the soft tissue is compressed against the bone surface by tying the suture ends into a knot. When the soft tissue is directly compressed against a bony surface, the body's healing response will affix the soft tissue to the bone to complete the repair. In the case of an implant pulling out of the bone there is a piece of hard material from that implant floating inside the joint space. That piece of material could temporary or permanently be stuck within the joint, causing damage to the articulating surfaces.
Many surgeons are beginning to favor using all-suture suture anchors over traditional suture anchors. One particular advantage of using an all-suture anchor is that it requires a smaller hole to be drilled to the bone. Preserving bone is preferred by surgeons. There are quite a few all-suture anchor designs on the market today intended to capture this trend.
The JuggerKnot™, by Biomet, has its anchor configuration made of a section of #5-polyester suture. The loaded suture is inserted through the length of the #5 suture section of the anchor. The anchor is preloaded on an inserter at the middle point. The inserter pushes the anchor into a drilled hole in the bone until a desired position is reached. The inserter is then removed. Both suture limbs are lightly pulled to contract the anchor, expanding it laterally against the wall of the drilled hole. This design relies on the friction between the suture ball of the anchor and the bone. Depending upon the position inside the hole to which the anchor is deployed or set, anchor slippage may occur when higher tension applied on the anchor until the anchor may move to a harder bone surface such as the cortex.
ConMed Linvatec also has introduced an anchor called the Y-Knot™. The anchor is very much the same construct as the Biomet JuggerKnot anchor in terms of design, but with different suture material. It uses high-strength suture for the anchor instead of polyester suture. The technique for using the anchor is also very similar as the company suggests in its own words: “Drill Pilot Hole, Insert Anchor, and Pull-to set.” Since the anchor designs and techniques are similar, the anchor shares the same weakness of relying on friction. Thus, slippage can occur, and pull out strength could not be adequate.
Another similar anchor is from Stryker and is called Iconix™. The anchor is designed to have opening sections along the sheet portion, which claim to provide a bunching effect using targeted compression zones. The middle point of the anchor is also preloaded on an inserter and inserted into a pre-drilled hole. When deployed by applying tension on the pre-loaded suture limbs, instead of the whole section of the anchor expanding randomly within the hole, those opening sections on the anchor are intended to swing outward laterally up to 3 mm-4 mm. However, such claimed expansion dimensions are theoretical only, because the soft suture is not stiff enough to penetrate the hole to achieve such dimensions in practice.
All of the foregoing anchors are offered in different sizes (defined by the size of the hole drilled into the bone) and are pre-loaded with different sizes and numbers of floating sutures. All of these anchors, as noted above, are similar in construction: a floating suture or sutures are passed through a tube of larger suture. There may be one or more windows cut in the tube to allow the construct to bend at certain locations, as well as to allow the floating sutures to pass between the inside and outside of the tube. All of the anchors are then loaded onto similar inserters meant to push the anchor into a tunnel drilled into the bone. The anchors are wrapped around the top of the inserter shaft and secured in a fork at the tip. The floating sutures are routed along the inserter shaft and are secured in a cleat in the inserter handle.
Advantages of all-suture anchors that have resulted in their increased popularity in orthopedic procedures include:
a) the need for a smaller bone tunnel, because all-suture anchors deploy and change shape inside the bone tunnel, meaning that the drilled hole can be smaller than for rigid anchors with similar strength. This results in less bone removal and the ability to place anchors closer together when necessary;b) ease of revision, because if an all-suture anchor does not deploy correctly, or if the surgeon is not comfortable with the bone quality after drilling the bone tunnel, the small hole allows the practitioner to drill a slightly larger hole in the same location and to use a traditional rigid anchor. If the anchor is deployed, it is easy for the surgeon to drill through or remove the anchor in order to implant another one; andc) patient safety. In some cases, anchors can back out or be pulled out of the bone by patient activity or re-injury. If the anchor is located in a joint space, such as in the glenoid, and it pulls out of the bone after surgery, the soft material will not damage the bone surfaces (such as the humeral head) as can be the case with a rigid anchor.
All of the foregoing anchors are also deployed in similar manners. Once the anchor is placed at the bottom of the bone tunnel, the floating sutures are removed from the inserter handle and the inserter is removed. To deploy the anchor, the physician is required to pull on the floating sutures. This tension applied to the floating sutures pulls the anchor upwardly in the bone tunnel, and the friction between the anchor and the bone causes the anchor to change shape and expand to create an interference fit in the tunnel. In addition, the larger diameter of the anchor prevents it from pulling up through the smaller hole in the harder cortical bone near the surface. The floating sutures are then passed through soft tissue and the remaining procedural steps are identical to those of any other pre-loaded suture anchor.
Currently available all-suture anchors require manual tensioning by the practitioner in order to deploy the anchor, as noted above. Often, to avoid anchor pullout in soft bone, the practitioner will pull gently on one suture limb, then pull on the other, and back and forth in like manner until the anchor is deployed. The amount of tension required to fully deploy the anchor depends upon the bone quality, as well as practitioner skill, training, and experience. At a minimum, this results in inconsistent tension applied to deploy the anchor. This, in turn, will lead to inconsistent performance, both in cyclic displacement and ultimate pull-out strength. If the practitioner is concerned about the bone quality and only pulls gently to deploy the anchor (to avoid pulling the anchor out), the anchor displacement under cyclic loading will be greater and the ultimate pullout force could be reduced. Another failure mode is the anchor not expanding properly and pulling out of the bone tunnel during practitioner tensioning. This can happen if the bone is very hard and the anchor cannot properly expand, or if the bone is very soft and the practitioner pulls hard enough to overcome the maximum pullout force of the anchor.